Elastic wave device, high frequency front-end circuit, and communication apparatus

ABSTRACT

An elastic wave device includes an LiNbO3 substrate, a first elastic wave resonator including a first IDT electrode and a first dielectric film, and a second elastic wave resonator including a second IDT electrode and a second dielectric film. A Rayleigh wave travels along at least one surface of the elastic wave device. A thickness of the first dielectric film differs from a thickness of the second dielectric film. A propagation direction of an elastic wave in the first elastic wave resonator coincides with a propagation direction of an elastic wave in the second elastic wave resonator. Euler angles of the LiNbO3 substrate fall within a range of (0°±5°, θ, 0°±10°).

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2016-246267 filed on Dec. 20, 2016 and is a ContinuationApplication of PCT Application No. PCT/JP2017/037558 filed on Oct. 17,2017. The entire contents of each application are hereby incorporatedherein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an elastic wave device using a Rayleighwave, a high frequency front-end circuit including the elastic wavedevice, and a communication apparatus.

2. Description of the Related Art

Each of International Publication No. 2012/098816 and InternationalPublication No. 2007/125734 discloses an elastic wave device using aRayleigh wave.

The elastic wave device of International Publication No. 2012/098816includes a series arm resonator and a parallel arm resonator eachincluding an elastic wave resonator. In order to provide a filter devicehaving a steep filter characteristic and a wide pass band, thicknessesof silicon oxide films defining the elastic wave resonators aredifferent between the series arm resonator and the parallel armresonator. Moreover, in order to reduce or prevent spurious noise withinthe pass band, the propagation direction of an elastic wave in theelastic wave resonator defining the series arm resonator is differentfrom the propagation direction of an elastic wave in the elastic waveresonator defining the parallel arm resonator.

The elastic wave device disclosed in International Publication No.2007/125734 is provided with an LiNbO₃ substrate and an electrodeincluding an IDT (interdigital transducer) electrode mainly containingAu. It is described in International Publication No. 2007/125734 that θof Euler angles (φ, θ, ψ) of the LiNbO₃ substrate and a thickness of theelectrode have a specific relationship.

However, as described in International Publication No. 2012/098816, in acase where propagation directions of elastic waves are different fromeach other in a plurality of elastic wave resonators, the efficiency inarrangement of the elastic wave resonators on a chip is lowered, and itis difficult to miniaturize the elastic wave device.

Further, in a case where the propagation directions of elastic waves aredifferent from each other in a plurality of elastic wave resonatorsincluding silicon oxide films of different thicknesses, spurious noiseother than the target spurious noise to be reduced or prevented isgenerated within the pass band or in a vicinity of the pass band in somecases.

In International Publication No. 2007/125734, since the above-describedspecific relationship between the Euler angle θ and the electrodethickness holds across a wide range, in a case where the thicknesses ofsilicon oxide are different from each other in a plurality of elasticwave resonators, spurious noise caused by SH (Shear Horizontal) wavesmay be generated.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide elastic wavedevices that are each capable of significantly reducing or preventingspurious noise caused by SH waves while providing a reduction in size,and has a steep filter characteristic and a wide pass band, to provide ahigh frequency front-end circuit including the above elastic wavedevice, and to provide a communication apparatus.

An elastic wave device according to a preferred embodiment of thepresent invention includes an LiNbO₃ substrate; a first elastic waveresonator including a first IDT electrode provided on the LiNbO₃substrate and a first dielectric film provided to cover the first IDTelectrode; and a second elastic wave resonator including a second IDTelectrode provided on the LiNbO₃ substrate and a second dielectric filmprovided to cover the second IDT electrode. In the elastic wave device,a Rayleigh wave is used; a thickness of the first dielectric filmdiffers from a thickness of the second dielectric film; a propagationdirection of an elastic wave in the first elastic wave resonatorcoincides with a propagation direction of an elastic wave in the secondelastic wave resonator; Euler angles (φ, θ, ψ) of the LiNbO₃ substratefall within a range of (0°±5°, θ, 0°±10°); each of the first IDTelectrode and the second IDT electrode includes a main electrode; in acase where a thickness of the main electrode normalized by a wave lengthλ that is determined by an electrode finger pitch of at least one of thefirst IDT electrode and the second IDT electrode is denoted as T, and adensity ratio (ρ/ρ_(Pt)) of density of the main electrode (φ to densityof Pt (ρ_(Pt)) is denoted as r, θ of the Euler angles (φ, θ, ψ) of theLiNbO₃ substrate satisfies the following expression (1) in a range of0.055λ≤T×r≤0.10λ.

−0.033/(T×r−0.037)+29.99≤θ≤−0.050/(T×r−0.043)+32.45  (1)

In an elastic wave device according to a preferred embodiment of thepresent invention, the first IDT electrode and the second IDT electrodeinclude the same electrode material and have the same or substantiallythe same thickness.

In an elastic wave device according to a preferred embodiment of thepresent invention, ψ of the Euler angles (φ, θ, ψ) of the LiNbO₃substrate falls within a range from about −2° to about 2°. In this case,it is possible to significantly reduce or prevent spurious noisedifferent from the spurious noise caused by SH waves.

In an elastic wave device according to a preferred embodiment of thepresent invention, each of the first dielectric film and the seconddielectric film mainly contains silicon oxide. In this case, frequencytemperature characteristics may be further improved

In an elastic wave device according to a preferred embodiment of thepresent invention, the first elastic wave resonator is a series armresonator and the second elastic wave resonator is a parallel armresonator, and a ladder filter is defined at least by the first elasticwave resonator and the second elastic wave resonator.

In an elastic wave device according to a preferred embodiment of thepresent invention, the elastic wave device is a duplexer that includes atransmission filter including the first elastic wave resonator, and areception filter including the second elastic wave resonator.

A high frequency front-end circuit according to a preferred embodimentof the present invention includes an elastic wave device according to apreferred embodiment of the present invention and a power amplifier.

A communication apparatus according to a preferred embodiment of thepresent invention includes a high frequency front-end circuit accordingto a preferred embodiment of the present invention and an RF signalprocessing circuit.

Preferred embodiments of the present invention provide elastic wavedevices, high frequency front-end circuits, and communicationapparatuses, in which the elastic wave device is capable ofsignificantly reducing or preventing spurious noise caused by SH waveswhile providing a reduction in size, and has a steep filtercharacteristic and a wide pass band.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of an elastic wave device according to apreferred embodiment of the present invention.

FIG. 2A is a circuit diagram of an elastic wave device according to apreferred embodiment of the present invention, and

FIG. 2B is a schematic plan view illustrating an electrode structure ofa one-port type elastic wave resonator.

FIG. 3 is a schematic cross-sectional view illustrating a first elasticwave resonator defining a series arm resonator in an elastic wave deviceaccording to a preferred embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view illustrating a second elasticwave resonator defining a parallel arm resonator in an elastic wavedevice according to a preferred embodiment of the present invention.

FIG. 5 is a schematic plan view when a propagation direction of anelastic wave in the second elastic wave resonator is slanted by about 1°relative to a propagation direction of an elastic wave in the firstelastic wave resonator.

FIG. 6 is a schematic plan view when a propagation direction of anelastic wave in the second elastic wave resonator is slanted by about 2°relative to a propagation direction of an elastic wave in the firstelastic wave resonator.

FIG. 7A is a graph showing impedance characteristics of a case where athickness of an SiO₂ film is about 0.2λ, and FIG. 7B is a graph showingreturn loss characteristics thereof.

FIG. 8A is a graph showing impedance characteristics of a case where athickness of an SiO₂ film is about 0.3λ, and FIG. 8B is a graph showingreturn loss characteristics thereof.

FIG. 9A is a graph showing impedance characteristics of a case where athickness of an SiO₂ film is about 0.4λ, and FIG. 9B is a graph showingreturn loss characteristics thereof.

FIG. 10A is a graph showing impedance characteristics of a case where athickness of an SiO₂ film is about 0.5λ, and FIG. 10B is a graph showingreturn loss characteristics thereof.

FIG. 11A is a graph showing impedance characteristics of a case where athickness of an SiO₂ film is about 0.6λ, and FIG. 11B is a graph showingreturn loss characteristics thereof.

FIG. 12A is a graph showing impedance characteristics of a case where θof Euler angles is about 27.5°, and FIG. 12B is a graph showing returnloss characteristics thereof.

FIG. 13A is a graph showing impedance characteristics of a case where θof Euler angles is about 28.0°, and FIG. 13B is a graph showing returnloss characteristics thereof.

FIG. 14A is a graph showing impedance characteristics of a case where θof Euler angles is about 28.5°, and FIG. 14B is a graph showing returnloss characteristics thereof.

FIG. 15A is a graph showing impedance characteristics of a case where θof Euler angles is about 29.0°, and FIG. 15B is a graph showing returnloss characteristics thereof.

FIG. 16A is a graph showing impedance characteristics of a case where θof Euler angles is about 29.5°, and FIG. 16B is a graph showing returnloss characteristics thereof.

FIG. 17A is a graph showing impedance characteristics of a case where θof Euler angles is about 30.0°, and FIG. 17B is a graph showing returnloss characteristics thereof.

FIG. 18A is a graph showing impedance characteristics of a case where θof Euler angles is about 30.5°, and FIG. 18B is a graph showing returnloss characteristics thereof.

FIG. 19A is a graph showing impedance characteristics of a case where θof Euler angles is about 31.0°, and FIG. 19B is a graph showing returnloss characteristics thereof.

FIG. 20A is a graph showing impedance characteristics of a case where θof Euler angles is about 31.5°, and FIG. 20B is a graph showing returnloss characteristics thereof.

FIG. 21 is a graph showing a relationship between θ of Euler angles anda fractional band width of SH waves.

FIG. 22 is a graph showing a relationship between θ of Euler angles anda fractional band width of SH waves when the thickness of an SiO₂ filmis varied.

FIG. 23 is a graph showing a relationship between θ of Euler angles anda thickness of a Pt film.

FIG. 24A is a graph showing impedance characteristics of a case where ivof Euler angles is about 0°, and FIG. 24B is a graph showing return losscharacteristics thereof.

FIG. 25A is a graph showing impedance characteristics of a case where ivof Euler angles is about 2°, and FIG. 25B is a graph showing return losscharacteristics thereof.

FIG. 26A is a graph showing impedance characteristics of a case where ivof Euler angles is about 4°, and FIG. 26B is a graph showing return losscharacteristics thereof.

FIG. 27 is a diagram of a communication apparatus and a high frequencyfront-end circuit according to a preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

It should be noted that the preferred embodiments described in thepresent specification are illustrative, and that the configurations andarrangements may be partially replaced or combined between differentpreferred embodiments.

Elastic Wave Device

FIG. 1 is a schematic plan view of an elastic wave device according to apreferred embodiment of the present invention. FIG. 2A is a circuitdiagram of an elastic wave device according to a preferred embodiment ofthe present invention. FIG. 2B is a schematic plan view illustrating anelectrode structure of a one-port type elastic wave resonator.

As illustrated in FIG. 1, an elastic wave device 1 includes an LiNbO₃substrate 2 as a piezoelectric substrate. A transmission filter 3 and areception filter 4 are provided on the LiNbO₃ substrate 2. The elasticwave device 1 is preferably, for example, a duplexer including thetransmission filter 3 and the reception filter 4. The elastic wavedevice 1 makes use of a Rayleigh wave. That is, a Rayleigh wave travelsalong at least one surface of the elastic wave device 1.

As illustrated in FIG. 2A, the elastic wave device 1 includes an antennaterminal 5. A shared terminal 6 is electrically connected to the antennaterminal 5. The transmission filter 3 is provided between the sharedterminal 6 and a transmission terminal 7. The reception filter 4 isprovided between the shared terminal 6 and a reception terminal 8.

The transmission filter 3 is preferably a ladder circuit, for example.Specifically, the transmission filter 3 includes series arm resonatorsS1 to S4 and parallel arm resonators P1 to P4. The series arm resonatorsS1 to S4 are electrically connected in series between the antennaterminal 5 and the transmission terminal 7. Note that in FIG. 1, theseries arm resonators S1 to S4 and the parallel arm resonators P1 to P4are indicated by a symbol in which an “X” mark is surrounded by arectangular frame.

Referring back to FIGS. 2A and 2B, the parallel arm resonator P1 iselectrically connected between an electrical connection point of thetransmission terminal 7 and the series arm resonator S1, and a groundpotential. The parallel arm resonator P2 is electrically connectedbetween an electrical connection point of the series arm resonator S1and the series arm resonator S2, and the ground potential. The parallelarm resonator P3 is electrically connected between an electricalconnection point of the series arm resonator S2 and the series armresonator S3, and the ground potential. The parallel arm resonator P4 iselectrically connected between an electrical connection point of theseries arm resonator S3 and the series arm resonator S4, and the groundpotential.

The series arm resonators S1 to S4 and the parallel arm resonators P1 toP4 are each preferably defined by a one-port type elastic waveresonator, for example.

The one-port type elastic wave resonator includes an electrode structureas illustrated in FIG. 2B. Specifically, an IDT electrode 9 andreflectors 10, 11 located on both sides in the elastic wave propagationdirection of the IDT electrode 9, are provided on the LiNbO₃ substrate2. With this, the one-port type elastic wave resonator is provided.

Note that the reflectors 10, 11 may not be provided.

Meanwhile, in the reception filter 4, a one-port type elastic waveresonator 12 defining a trap is electrically connected to the sharedterminal 6. Three-IDT longitudinally coupled resonator elastic wavefilter units 13 and 14 are provided between the one-port elastic waveresonator 12 and the reception terminal 8. The longitudinally coupledresonator elastic wave filter units 13 and 14 are electrically connectedto each other in a cascading electrical connection. Each of thelongitudinally coupled resonator elastic wave filter units 13 and 14includes three IDT electrodes. The longitudinally coupled resonatorelastic wave filter units 13 and 14 may be a five-IDT type includingfive IDT electrodes, or may be an n-IDT type including n IDT electrodes(n≥1).

Although the transmission filter 3 includes a ladder circuit and thereception filter 4 includes a longitudinally coupled resonator elasticwave filter, the transmission filter 3 may include a longitudinallycoupled resonator elastic wave filter and the reception filter 4 mayinclude a ladder circuit.

Next, elastic wave resonators defining the series arm resonators S1 toS4 and the parallel arm resonators P1 to P4 will be described withreference to FIG. 3 and FIG. 4.

FIG. 3 is a schematic cross-sectional view illustrating a first elasticwave resonator defining a series arm resonator in an elastic wave deviceaccording to a preferred embodiment of the present invention. FIG. 4 isa schematic cross-sectional view illustrating a second elastic waveresonator defining a parallel arm resonator in an elastic wave deviceaccording to a preferred embodiment of the present invention.

As illustrated in FIG. 3, a first elastic wave resonator 20 includes aLiNbO₃ substrate 2, a first IDT electrode 21, a first dielectric film22, and a first frequency adjustment film 23. The first IDT electrode 21is provided on a main surface 2 a of the LiNbO₃ substrate 2. The firstdielectric film 22 covers the first IDT electrode 21. The firstfrequency adjustment film 23 is provided on the first dielectric film22.

As illustrated in FIG. 4, a second elastic wave resonator 30 includesthe LiNbO₃ substrate 2, a second IDT electrode 31, a second dielectricfilm 32, and a second frequency adjustment film 33. The second IDTelectrode 31 is provided on the main surface 2 a of the LiNbO₃ substrate2. The second dielectric film 32 covers the second IDT electrode 31. Thesecond frequency adjustment film 33 is provided on the second dielectricfilm 32. The first elastic wave resonator 20 and the second elastic waveresonator 30 share the LiNbO₃ substrate 2.

As illustrated in FIGS. 3 and 4, a thickness t1 of the first dielectricfilm 22 in the first elastic wave resonator 20 is preferably thickerthan a thickness t2 of the second dielectric film 32 in the secondelastic wave resonator 30 (t1≥t2). However, the thickness t2 of thesecond dielectric film 32 may be thicker than the thickness t1 of thefirst dielectric film 22. In other words, it is sufficient that thethickness t1 of the first dielectric film 22 is different from thethickness t2 of the second dielectric film 32. As discussed above, inthe present preferred embodiment, since the thickness t1 of the firstdielectric film 22 and the thickness t2 of the second dielectric film 32are different from each other, steepness is able to be enhanced in thefilter characteristic, and the pass band width is able to be widened.

For example, in order to provide a filter characteristic having highsteepness at a higher frequency side of the pass band in a ladderfilter, it is preferable to reduce Δf (a difference between a resonantfrequency and an anti-resonant frequency) of an elastic wave resonatordefining a series arm resonator. Since Δf is able to be reduced byincreasing the film thickness of the dielectric film covering the mainsurface of the piezoelectric substrate (LiNbO₃ substrate) and the IDTelectrode, the film thickness of the dielectric film on the series armresonator is increased. On the other hand, in a case of using an elasticwave resonator with Δf being small, the band width of the filter isreduced, and it is preferable, for example, to increase Δf of theelastic wave resonator defining the parallel arm resonator. For thispurpose, the film thickness of the dielectric film on the parallel armresonator is reduced.

Meanwhile, in order to provide a filter characteristic having highsteepness at a lower frequency side of the pass band, it is preferableto reduce Δf of an elastic wave resonator defining a parallel armresonator. For this purpose, the film thickness of the dielectric filmon the parallel arm resonator is increased. In contrast, in order towiden the band width of the filter, the film thickness of the dielectricfilm on the series arm resonator is reduced, thus increasing Δf of theseries arm resonator.

Then, by setting the film thicknesses of the dielectric films to bedifferent from each other between the series arm resonator and theparallel arm resonator as described above, steepness in the filtercharacteristic is able to be enhanced, and the pass band width is ableto be widened.

The above description applies not only to a ladder filter, but alsosimilarly applies to a longitudinally coupled resonator elastic wavefilter. In this case, for example, by setting the thickness of adielectric film covering an IDT electrode in the one-port type elasticwave resonator 12 in FIG. 2A to be thicker than the thicknesses ofdielectric films covering IDT electrodes in the longitudinally coupledresonator elastic wave filter units 13 and 14, steepness in the filtercharacteristic is able to be enhanced and the pass band width is able tobe widened.

As described above, in the present preferred embodiment, since thethickness t1 of the first dielectric film 22 differs from the thicknesst2 of the second dielectric film 32, steepness in the filtercharacteristic is able to be enhanced and the pass band width is able tobe widened.

Note that there is no particular limitation on a method by which thethickness t1 of the first dielectric film 22 and the thickness t2 of thesecond dielectric film 32 are different from each other on the identicalLiNbO₃ substrate 2, and a non-limiting method as follows may be used,for example.

First, the first IDT electrode 21 and the second IDT electrode 31 areformed on the LiNbO₃ substrate 2. At the time of forming the first IDTelectrode 21 and the second IDT electrode 31, the first IDT electrode 21and the second IDT electrode 31 are film-formed simultaneously orsubstantially simultaneously. Therefore, the first IDT electrode 21 andthe second IDT electrode include the same electrode material and havethe same or substantially the same thickness.

Here, since the electrode material of the first IDT electrode 21 is thesame as the electrode material of the second IDT electrode 31, the firstIDT electrode 21 and the second IDT electrode 31 are film-formed at thesame time, including a case where impurities are mixed in the materialduring the manufacturing process, or the like.

In addition, since the thickness of the first IDT electrode 21 is thesame or substantially the same as the thickness of the second IDTelectrode 31, the first IDT electrode 21 and the second IDT electrode 31are film-formed at the same time, an error in thickness generated duringthe manufacturing process, mounting process, or the like is alsoincluded.

A dielectric film is formed to cover the first IDT electrode 21 and thesecond IDT electrode 31 on the LiNbO₃ substrate 2. Subsequently, aresist film is formed on the dielectric film of the elastic waveresonator whose thickness is to be large. Next, by etching thedielectric film, the thickness of a portion of the dielectric film wherethe resist film is not formed is reduced. Finally, the resist film isremoved to provide dielectric films with different thicknesses.

Further, after the dielectric film is formed on the LiNbO₃ substrate 2,a resist film may be formed on the dielectric film of the elastic waveresonator whose thickness is to be small, and then a dielectric film maybe further film-formed thereon. Also in this case, dielectric films withdifferent thicknesses are able to be provided by removing the resist.

In the present preferred embodiment, all of the series arm resonators S1to S4 are defined by the first elastic wave resonator 20. Further, allof the parallel arm resonators P1 to P4 are defined by the secondelastic wave resonator 30. Note that, however, it is sufficient that atleast one of the series arm resonators S1 to S4 is defined by the firstelastic wave resonator 20. Further, it is sufficient that at least oneof the parallel arm resonators P1 to P4 is defined by the second elasticwave resonator 30. In addition, at least one resonator defining thetransmission filter 3 may be defined by the first elastic wave resonator20, and at least one resonator defining the reception filter 4 may bedefined by the second elastic wave resonator 30. In any case, theadvantageous effects of the present invention are able to be provided.

The first IDT electrode 21 and the second IDT electrode 31 preferablyinclude the same electrode material and have the same or substantiallythe same thickness.

The material of the first IDT electrode 21 and the second IDT electrode31 is not particularly limited, and examples thereof include Au, Pt, Ag,Ta, W, Ni, Ru, Pd, Cr, Mo, Zn, Ti, Ni, Cr, Cu, Al, and an alloy of thesemetals. The first IDT electrode 21 and the second IDT electrode 31 maybe a single-layer metal film or a laminated metal film in which two ormore kinds of metal films are laminated.

In the present preferred embodiment, each of the first IDT electrode 21and the second IDT electrode 31 is preferably a laminated metal film inwhich a close contact layer 41, a main electrode 42, a close contactlayer 43, a conductive auxiliary film 44, and a close contact layer 45are laminated in that order from the LiNbO₃ substrate 2 side. The mainelectrode 42 is an electrode layer that occupies the largest mass in theIDT electrode.

As a material of the close contact layers 41, 43, and 45, for example,Ti, Cr, or NiCr may preferably be included.

The material of the main electrode 42 is not particularly limited, and ametal having a relatively high density such as Au, Pt, Ag, Ta, W, Ni,Ru, Pd, Cr, Mo, Zn or Cu, or an alloy of these metals may preferably beincluded.

The material of the conductive auxiliary film 44 is not particularlylimited, and Al, Cu, or an alloy thereof may preferably be included, forexample.

Note that the close contact layers 41, 43 and 45, and the conductiveauxiliary film 44 may not be provided.

The first dielectric film 22 and the second dielectric film 32 improvefrequency temperature characteristics. The material of the firstdielectric film 22 and the second dielectric film 32 is not particularlylimited, and a material containing, for example, silicon oxide orsilicon oxynitride as a primary component may be included. In thisspecification, the primary component refers to a component contained inan amount of equal to or more than about 50%. In the present preferredembodiment, both of the first dielectric film 22 and the seconddielectric film 32 are preferably a silicon oxide film, for example.

The first frequency adjustment film 23 and the second frequencyadjustment film 33 adjust frequencies. The material of the firstfrequency adjustment film 23 and the second frequency adjustment film 33is not particularly limited, and silicon nitride or aluminum oxide, forexample, may preferably be included. In the present preferredembodiment, both of the first frequency adjustment film 23 and thesecond frequency adjustment film 33 are preferably a silicon nitridefilm, for example.

Note that the first frequency adjustment film 23 and the secondfrequency adjustment film 33 may not be provided.

In the elastic wave device 1, the propagation direction of the elasticwave in the first elastic wave resonator 20 defining the series armresonators S1 to S4 coincides with the propagation direction of theelastic wave in the second elastic wave resonator defining the parallelarm resonators P1 to P4. More specifically, the propagation direction ofthe elastic wave in the first elastic wave resonator 20 is a propagationdirection A1 as illustrated in FIG. 1. The propagation direction of theelastic wave in the second elastic wave resonator 30 is a propagationdirection A2 as illustrated in FIG. 1. In FIG. 1, the propagationdirection A1 and the propagation direction A2 coincide with each other.In this specification, the expression “to coincide with each other”means a situation in which an angle between the propagation direction A1and the propagation direction A2 falls within a range smaller than about2°, and also includes a case where the propagation direction A1 and thepropagation direction A2 does not completely coincide. However, in thepresent preferred embodiment, the propagation direction A1 preferablycompletely coincides with the propagation direction A2.

As described above, in the elastic wave device 1, since the propagationdirection A1 of the elastic wave in the first elastic wave resonator 20coincides with the propagation direction A2 of the elastic wave in thesecond elastic wave resonator 30, it is possible to miniaturize theelastic wave device 1.

In the present preferred embodiment, Euler angles (φ, θ, ψ) of theLiNbO₃ substrate 2 preferably fall within a range of (0°±5°, θ, 0°±10°),for example. In particular, θ of the Euler angles (φ, θ, ψ) of theLiNbO₃ substrate 2 satisfies the following expression (1) in a range ofabout 0.055λ≤T×r≥ about 0.10λ. Note that T is a thickness of the mainelectrode 42 of each of the first IDT electrode 21 and the second IDTelectrode 31.

Although the first IDT electrode 21 and the second IDT electrode 31preferably include the same electrode material and to have the same orsubstantially the same thickness, a portion of the components of theelectrode material may change to different matter or the film thicknessthereof may change to a different value during the manufacturingprocess, mounting process, or the like. In such case, any of theelectrodes may take the thickness T, or any of the electrodes may takedensity r. In this specification, the thickness refers to a thicknessnormalized by a wave length λ that is determined by an electrode fingerpitch of the IDT electrode. Further, r is a density ratio (ρ/ρ_(Pt)) ofdensity of the main electrode 42 (ρ) to density of Pt (ρ_(Pt)).

−0.033/(T×r−0.037)+29.99≤θ≤−0.050/(T×r−0.043)+32.45  (1)

In the present preferred embodiment, since θ of the Euler angles of theLiNbO₃ substrate 2 falls within the above range, spurious noise causedby SH waves may be significantly reduced or prevented. Accordingly, withthe elastic wave device 1, a steep filter characteristic and a wide passband may be provided, and a significant reduction or prevention ofspurious noise caused by SH waves is able to be provided while providingthe miniaturization.

Preferably, for example, ψ of the Euler angles (φ, θ, ψ) of the LiNbO₃substrate 2 fall within a range from about −2° to about 2°. When ψ ofthe Euler angles falls within the above range, it is possible to furthersignificantly reduce or prevent spurious noise that is different fromthe spurious noise caused by the SH waves.

Next, the miniaturization provided by causing the propagation directionA1 and the propagation direction A2 to coincide with each other isdescribed with reference to FIG. 5 and FIG. 6.

FIG. 5 is a schematic plan view when the propagation direction of theelastic wave in the second elastic wave resonator is slanted by about 1°relative to the propagation direction of the elastic wave in the firstelastic wave resonator. FIG. 6 is a schematic plan view when thepropagation direction of the elastic wave in the second elastic waveresonator is slanted by about 2° relative to the propagation directionof the elastic wave in the first elastic wave resonator. In FIGS. 5 and6, an end portion 2 b in an outer side portion relative to a broken linein the LiNbO₃ substrate 2 is a portion where an electrode pattern is notable to be provided.

As illustrated in FIGS. 5 and 6, when the propagation direction A2 ofthe elastic wave in the second elastic wave resonator 30 is slanted, theparallel arm resonators P1 to P4 each defined by the elastic waveresonator 30 are slanted by the same or substantially the same angle.

As illustrated in FIG. 5, when the parallel arm resonators P1 to P4 areslanted by about 1°, the parallel arm resonators P1 to P4 do not reachthe end portion 2 b where the electrode pattern is not able to beprovided. On the other hand, as illustrated in FIG. 6, when the parallelarm resonators P1 to P4 are slanted by about 2°, the parallel armresonators P1 to P4 reach the end portion 2 b where the electrodepattern is not able to be provided. When the parallel arm resonators P1to P4 are slanted by about 2°, they may overlap with the series armresonators S1 to S4 or pattern wiring 15. Accordingly, when the parallelarm resonators P1 to P4 are slanted by about 2° or more, a space thatincludes the resonators or the pattern wiring 15 is enlarged, andminiaturization is not able to be easily provided. In a case where thewidth of the pattern wiring 15 is reduced in order to secure the space,electrical resistance of the pattern wiring 15 is increased, and thecharacteristics of the elastic wave device 1 may be deteriorated.

In contrast, in the present preferred embodiment, the angle between thepropagation direction A1 of the elastic wave in the first elastic waveresonator 20 and the propagation direction A2 of the elastic wave in thesecond elastic wave resonator 30 falls within a range smaller than about2°, and the propagation directions A1 and A2 coincide with each other.Therefore, the elastic wave device 1 is able to be reduced in size, andthe deterioration in characteristics is unlikely to occur.

Next, with reference to FIGS. 7A to 23, spurious noise caused by SHwaves being significantly reduced or prevented by setting θ of the Eulerangles of the LiNbO₃ substrate 2 within a specific range is described.

First, with the structure illustrated in FIG. 3, an elastic waveresonator is designed as follows. In the designed elastic waveresonator, the close contact layers 41, 43, and 45 are not included.

-   -   LiNbO₃ substrate 2—Euler angles (0°, 30°, 0°)    -   First IDT electrode 21—duty ratio: about 0.60    -   Main electrode 42—Pt film, thickness: about 0.075λ    -   Conductive auxiliary film 44—Al film, thickness: about 0.08λ    -   First dielectric film 22—SiO₂ film, thickness: adjusted in a        range of about 0.2λ to about 0.6λ    -   First frequency adjustment film 23—SiN film, thickness: about        0.01λ    -   Elastic wave—Rayleigh wave

In the elastic wave resonator designed under the above conditions, θ ofthe Euler angles is fixed to about 30°, the thickness of the SiO₂ filmis varied within the range of about 0.2λ to about 0.6λ, and impedancecharacteristics and return loss characteristics are measured.

FIGS. 7A, 8A, 9A, 10A, and 11A are graphs showing impedancecharacteristics when the thickness of the SiO₂ film is varied, and FIGS.7B, 8B, 9B, 10B, and 11B are graphs showing return loss characteristicsthereof. The thickness of the SiO₂ film is 0.2λ, 0.3λ, 0.4λ, 0.5λ, and0.6λ in that order in FIGS. 7A to 11B.

As is apparent from FIGS. 7A to 11B, when 0 of the Euler angles is about30°, spurious noise caused by SH waves is significantly reduced orprevented in a vicinity of the band regardless of the thickness of theSiO₂ film.

Next, in the designed elastic wave resonator, the thickness of the SiO₂film is fixed to 0.3λ, θ of the Euler angles is varied within a range ofabout 27.5° to about 31.5°, and impedance characteristics and returnloss characteristics are measured.

In FIGS. 12A to 20B, each of FIGS. 12A, 13A, 14A, 15A, 16A, 17A, 18A,19A, and 20A is a graphs showing impedance characteristics when θ of theEuler angles is varied, and each of FIGS. 12B, 13B, 14B, 15B, 16B, 17B,18B, 19B, and 20B is a graph showing return loss characteristicsthereof. Note that, θ of the Euler angles is about 27.5°, about 28.0°,about 28.5°, about 29.0°, about 29.5°, about 30.0°, about 30.5°, about31.0°, and about 31.5° in that order in FIGS. 12A to 20B.

As is apparent from FIGS. 16A and 16B (θ=29.5°) and FIGS. 17A and 17B(θ=30.0°), when θ of the Euler angles is equal to or larger than about29.5° and equal to or smaller than about 30.0°, substantially nospurious noise caused by SH waves is generated. However, in a case ofmanufacturing an elastic wave device including a one-port type elasticwave resonator, a problem may occur when an absolute value of themagnitude of spurious noise caused by SH waves is greater than about 0.3dB. Therefore, it is preferable for the magnitude of spurious noise tobe equal to or smaller than about 0.3 dB in an absolute value. Asunderstood from FIGS. 12 to 20, θ of the Euler angles is equal to orlarger than about 28.5° and equal to or smaller than about 31.0° whenthe absolute value of the magnitude of spurious noise caused by SH wavesbecomes equal to or smaller than about 0.3 dB.

FIG. 21 is a graph showing a relationship between θ of Euler angles anda fractional band width of SH waves. FIG. 21 shows a result providedwhen an elastic wave resonator of the same or substantially the samedesign as the design in FIGS. 12A to 20B is included. The fractionalband width of SH waves is a value indicating the magnitude of spuriousnoise cause by the SH waves. FIG. 21 shows that, when θ of the Eulerangles is equal to or larger than about 28.5° and equal to or smallerthan about 31.0°, the fractional band width of the SH waves is equal toor smaller than about 0.005%. From this, it is understood that, when thefractional band width of the SH waves is equal to or smaller than about0.005%, the spurious noise caused by the SH waves is able to besufficiently reduced. Accordingly, the range of θ of the Euler angles inwhich the fractional band width of the SH waves is equal to or smallerthan about 0.005%, is a range of θ of the Euler angles capable ofsufficiently reducing the spurious noise caused by the SH waves.

In particular, in the present preferred embodiment, since the elasticwave resonators including SiO₂ films of different thicknesses areprovided, it is sufficient to determine a range of θ of the Euler anglesin which the fractional band width of SH waves becomes equal to or lessthan about 0.005% regardless of the thickness of the SiO₂ film. Therange of θ of the Euler angles in which the fractional band width of SHwaves becomes equal to or less than about 0.005% regardless of thethickness of the SiO₂ film, is a range of θ of the Euler angles capableof sufficiently reducing spurious noise caused by SH waves regardless ofthe thickness of the SiO₂ film.

FIG. 22 is a graph showing a relationship between θ of Euler angles anda fractional band width of SH waves when the thickness of the SiO₂ filmis varied. Note that FIG. 22 shows a result provided when an elasticwave resonator of the same or substantially the same design as thedesign in FIG. 21 is included, except that the thickness of the SiO₂film is varied.

Although an electromechanical coupling coefficient of SH waves isdifferent depending on the thickness of the SiO₂ film, it is understoodfrom FIG. 22 that, when θ of the Euler angles is equal to or larger thanabout 29.1° and equal to or smaller than about 30.9°, spurious noisecaused by the SH waves is able to be sufficiently reduced regardless ofthe thickness of the SiO₂ film.

Similarly, a lower limit value and an upper limit value of θ of Eulerangles provided by varying the thickness of a Pt film, which is the mainelectrode 42, are shown in Table 1 below. The lower limit values and theupper limit values of θ of the above-mentioned Euler angles are valuesat which the fractional band width of SH waves becomes equal to orsmaller than about 0.005% regardless of the thickness of the SiO₂ film.

TABLE 1 Pt film Lower limit Upper limit thickness value of θ value of θ(λ) (°) (°) 0.055 28.15 28.2 0.06 28.55 29.45 0.065 28.8 30.15 0.0728.95 30.6 0.075 29.1 30.9 0.08 29.2 31.15 0.085 29.25 31.3 0.09 29.331.45 0.095 29.35 31.55 0.1 29.4 31.6

FIG. 23 is a graph showing a relationship between θ of Euler angles andthe thickness of a Pt film. Note that FIG. 23 is a graph in which the Ptfilm thicknesses and the lower and upper limit values of θ of the Eulerangles in Table 1 are plotted. A curved line indicated by an arrow A inFIG. 23 is a curved line provided by plotting the lower limit values ofθ of the Euler angles. The curved line indicated by the arrow A isrepresented by an expression of −0.033/(T_(Pt)−0.037)+29.99, whereT_(pt) is the thickness of the Pt film. A curved line indicated by anarrow B in FIG. 23 is a curved line provided by plotting the upper limitvalues of θ of the Euler angles. The curved line indicated by the arrowB is represented by an expression of −0.050/(T_(Pt)−0.043)+32.45, whereT_(pt) is the thickness of the Pt film. In FIG. 23, a region surroundedby the curved line indicated by the arrow A and the curved lineindicated by the arrow B is a region in which the spurious noise causedby the SH waves is able to be sufficiently reduced. The followingexpression (2) represents the above-mentioned region where the spuriousnoise caused by the SH waves is able to be sufficiently reduced.

−0.033/(T _(Pt)−0.037)+29.99≤θ≤−0.050/(T _(Pt)−0.043)+32.45  expression(2)

An intersection point between the curved line indicated by the arrow Aand the curved line indicated by the arrow B corresponds to the lowerlimit value of the thickness of the Pt film, which is about 0.055λ. In acase where the thickness of the Pt film defining and functioning as themain electrode 42 becomes excessively large, the aspect ratio of the IDTelectrode becomes large, and the IDT electrode is not able to be easilyformed. Further, since there is a risk of causing voids, cracks, or thelike to be generated in the dielectric film on the IDT electrode, theupper limit of the Pt film thickness is determined to be 0.10λ.

In a case where a metal other than Pt is included as a material of themain electrode 42, the thickness of the main electrode 42 is changed byan amount of the density ratio of the metal and Pt. To be specific, in acase where the main electrode 42 of density ρ is included, the thicknessT of the main electrode 42 is set as follows: T=T_(Pt)×(ρ_(Pt)/ρ). Notethat, ρ_(Pt) is the density of Pt. In a case where ρ/ρ_(Pt) is taken asr (i.e., r=ρ/ρ_(Pt)) and an expression of T_(Pt)=T/(ρ_(Pt)/φ issubstituted into the expression (2), the result is represented with thefollowing expression (1).

−0.033/(T×r−0.037)+29.99≤θ≤−0.050/(T×r−0.043)+32.45  (1)

Note that (T×r) is set within a range of about 0.055λ≤T×r≤about 0.10λ.

From the above, it is understood that, by setting θ of the Euler angleswithin the range represented by the above expression (1), the spuriousnoise caused by the SH waves is able to be significantly reduced orprevented regardless of the thickness of the SiO₂ film. Since thespurious noise caused by the SH waves is able to be significantlyreduced or prevented regardless of the thickness of the SiO₂ film, evenin a case where the thicknesses of the first dielectric film 22 and thesecond dielectric film 32 are different from each other as in theelastic wave device 1, the spurious noise caused by the SH waves is ableto be significantly reduced or prevented.

Although FIGS. 7A to 23 show the results when the Euler angles (φ, θ, ψ)are (0°, θ, 0°), similar results are able to be provided also in a rangeof (0°±5°, θ, 0°±10°).

Next, with reference to FIGS. 24A to 26B, spurious noise different fromthe spurious noise caused by the SH waves being further significantlyreduced or prevented by setting ψ of Euler angles (φ, θ, ψ) to be withina specific range is described.

FIGS. 24A to 26B show the results provided when an elastic waveresonator designed as described below is used. In the designed elasticwave resonator, the close contact layers 41, 43, and 45 are notincluded.

-   -   LiNbO₃ substrate 2—Euler angles (0°, 30°, ψ°)    -   First IDT electrode 21—duty ratio: about 0.60    -   Main electrode 42—Pt film, thickness: about 0.075λ    -   Conductive auxiliary film 44—Al film, thickness: about 0.08λ    -   First dielectric film 22—SiO₂ film, thickness: about 0.3λ    -   First frequency adjustment film 23—SiN film, thickness: about        0.01λ

Each of FIGS. 24A, 25A, and 26A is a graph showing impedancecharacteristics when ψ of the Euler angles is varied, and each of FIGS.24B, 25B, and 26B is a graph showing return loss characteristicsthereof. Note that, ψ of the Euler angles is about 0°, about 2°, andabout 4° in that order in FIGS. 24A to 26B. From FIGS. 24A to 26B, it isunderstood that large spurious noise is generated near a normalizedfrequency 1.16 and near a normalized frequency 1.23 when the Euler angleψ is varied by about 4°. On the other hand, it is understood that, whenthe Euler angle ψ is varied by about 2° or less, spurious noise near thenormalized frequency 1.16 and near the normalized frequency 1.23 issignificantly reduced or prevented.

The above-described spurious noise is spurious noise generated due tothe symmetry of the LiNbO₃ substrate being broken with respect to thepropagation direction of the elastic wave by shifting the Euler angle ψfrom 0°. Therefore, it is preferable, for example, for ψ to be close to0°.

From this, it is understood that, by setting the Euler angle ψ to bewithin a range from about −2° to about 2°, spurious noise different fromthe spurious noise caused by the SH waves is able to be furthersignificantly reduced or prevented.

High Frequency Front-End Circuit and Communication Apparatus

The elastic wave device of the preferred embodiment described above isable to be included as a duplexer of a high frequency front-end circuitor the like. This example will be described below.

FIG. 27 is a diagram of a communication apparatus and a high frequencyfront-end circuit according to a preferred embodiment of the presentinvention. In FIG. 27, components and elements connected with a highfrequency front-end circuit 230, such as an antenna element 202 and anRF signal processing circuit (RFIC) 203, are also illustrated. The highfrequency front-end circuit 230 and the RF signal processing circuit 203define a communication apparatus 240. The communication apparatus 240may include a power supply, a CPU, a display, and the like, for example.

The high frequency front-end circuit 230 includes a switch 225,duplexers 201A and 201B, filters 231 and 232, low-noise amplificationcircuits 214 and 224, and power amplification circuits 234 a, 234 b, 244a, and 244 b. Note that the high frequency front-end circuit 230 and thecommunication apparatus 240 illustrated in FIG. 27 are examples of ahigh frequency front-end circuit and a communication apparatus, and arenot limited to this specific configuration and arrangement.

The duplexer 201A includes filters 211 and 212. The duplexer 201Bincludes filters 221 and 222. The duplexers 201A and 201B are connectedto the antenna element 202 via a switch 225. The elastic wave devicedescribed above may define and function as the duplexers 201A and 201B,and may define and function as the filters 211, 212, 221, and 222.

Further, the elastic wave device described above is also able to beapplied to a multiplexer including three or more filters, such as atriplexer in which an antenna terminal for three filters is shared and ahexaplexer in which an antenna terminal for six filters is shared.

In other words, the elastic wave device described above includes anelastic wave resonator, a filter, a duplexer, and a multiplexerincluding three or more filters. The multiplexer is not limited to botha transmission filter and a reception filter, and may include only atransmission filter or only a reception filter.

The switch 225 connects the antenna element 202 to a signal pathcorresponding to a predetermined band controlled by a control signalfrom a control unit (not illustrated), and is preferably defined by, forexample, a single pole double throw (SPDT) type switch. The number ofsignal paths connected to the antenna element 202 is not limited to one,and there may be a plurality of signal paths. That is, the highfrequency front-end circuit 230 may correspond to carrier aggregation.

The low-noise amplification circuit 214 is a reception amplificationcircuit that amplifies a high frequency signal (in this case, a highfrequency reception signal) traveling through the antenna element 202,the switch 225 and the duplexer 201A, and output the amplified highfrequency signal to the RF signal processing circuit 203. The low-noiseamplification circuit 224 is a reception amplification circuit thatamplifies a high frequency signal (in this case, a high frequencyreception signal) traveling through the antenna element 202, the switch225 and the duplexer 201B, and output the amplified high frequencysignal to the RF signal processing circuit 203.

The power amplification circuits 234 a and 234 b are transmissionamplification circuits that amplify a high frequency signal (in thiscase, a high frequency transmission signal) output from the RF signalprocessing circuit 203, and output the amplified high frequency signalto the antenna element 202 through the duplexer 201A and the switch 225.The power amplification circuits 244 a and 244 b are transmissionamplification circuits that amplify a high frequency signal (in thiscase, a high frequency transmission signal) output from the RF signalprocessing circuit 203, and output the amplified high frequency signalto the antenna element 202 through the duplexer 201B and the switch 225.

The RF signal processing circuit 203 performs signal processing on ahigh frequency reception signal input from the antenna element 202through a reception signal path by down-conversion or the like, andoutputs a reception signal generated by performing the signalprocessing. In addition, the RF signal processing circuit 203 performssignal processing on an input transmission signal by up-conversion orthe like, and outputs a high frequency transmission signal generated byperforming the signal processing to the power amplification circuits 234a, 234 b, 244 a, or 244 b. The RF signal processing circuit 203 ispreferably, for example, an RFIC. The communication apparatus mayinclude a baseband (BB) IC. In this case, the BBIC performs signalprocessing on the reception signal processed by the RFIC. Further, theBBIC performs signal processing on a transmission signal and outputs theprocessed signal to the RFIC. The reception signal processed by the BBICand the transmission signal before being signal-processed by the BBICare an image signal and a sound signal, for example. The high frequencyfront-end circuit 230 may include other circuit elements between theabove-described components and elements.

The high frequency front-end circuit 230 may include duplexers accordingto a modification of the duplexers 201A and 201B, in place of theduplexers 201A and 201B.

Meanwhile, the filters 231 and 232 in the communication apparatus 240are connected between the RF signal processing circuit 203 and theswitch 225 via none of the low-noise amplification circuits 214, 224 andthe power amplification circuits 234 a, 234 b, 244 a and 244 b. Thefilters 231 and 232 are also connected to the antenna element 202 viathe switch 225, similarly to the duplexers 201A and 201B.

According to the high frequency front-end circuit 230 and thecommunication apparatus 240 provided as described above, by including anelastic wave resonator, a filter, a duplexer, a multiplexer includingthree or more filters, and the like, each of which is a preferredembodiment of the elastic wave device of the present invention, spuriousnoise caused by the SH waves is able to be significantly reduced orprevented while providing the miniaturization, to enhance the steepnessin the filter characteristic, and to widen the pass band as well.

Thus far, the elastic wave devices, the high frequency front-endcircuits, and the communication apparatuses according to the preferredembodiments of the present invention have been described. However, thepresent invention also includes other preferred embodiments provided bycombining any components and elements in the above-described preferredembodiments, modifications provided by applying various modificationsand variations, which are able to be conceived by those skilled in theart, on the above-described preferred embodiments without departing fromthe spirit and scope of the present invention, and various kinds ofequipment incorporating the high frequency front-end circuit and thecommunication apparatus according to the present invention.

The preferred embodiments of the present invention are able to be widelyapplied to communication equipment such as a cellular phone, forexample, as an elastic wave resonator, a filter, a duplexer, amultiplexer applicable to a multi-band system, a front-end circuit, anda communication apparatus.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. An elastic wave device comprising: an LiNbO₃(Lithium Niobate) substrate; a first elastic wave resonator including afirst IDT (Interdigital Transducer) electrode provided on the LiNbO₃substrate and a first dielectric film provided to cover the first IDTelectrode; and a second elastic wave resonator including a second IDTelectrode provided on the LiNbO₃ substrate and a second dielectric filmprovided to cover the second IDT electrode; wherein a thickness of thefirst dielectric film is different from a thickness of the seconddielectric film; Euler angles (φ, θ, ψ) of the LiNbO₃ substrate fallwithin a range of (0°±5°, θ, 0°±10°); the first IDT electrode includes amain electrode that is an electrode layer that occupies a largest massin the first IDT electrode; and in a case where a thickness of the mainelectrode of the first IDT electrode normalized by a wave length λ₁ thatis determined by an electrode finger pitch of the first IDT electrode isdenoted as T₁, and a density ratio (ρ₁/ρ_(Pt)) of density of the mainelectrode of the first IDT electrode (ρ₁) to density of Pt (ρ_(Pt)) isdenoted as r₁, θ of the Euler angles (φ, θ, ψ) of the LiNbO₃ substratesatisfies the following expression (1) in a range of0.055λ≤T₁×r₁≤0.10λ₁:−0.033/(T ₁ ×r ₁−0.037)+29.99≤θ≤−0.050/(T ₁ ×r ₁−043)+32.45  (1).
 2. Theelastic wave device according to claim 1, wherein the first IDTelectrode and the second IDT electrode include a same electrode materialand have a same or substantially the same thickness.
 3. The elastic wavedevice according to claim 1, wherein the second IDT electrode includes amain electrode that is an electrode layer that occupies a largest massin the second IDT electrode; and in a case where a thickness of the mainelectrode of the second IDT electrode normalized by a wave length λ₂that is determined by an electrode finger pitch of the second IDTelectrode is denoted as T₂, and a density ratio (ρ₂/ρ_(Pt)) of densityof the main electrode of the second IDT electrode (ρ₂) to the density ofPt (ρ_(Pt)) is denoted as r₂, θ of the Euler angles (φ, θ, ψ) of theLiNbO₃ substrate satisfies the following expression (2) in a range of0.055λ₂≤T₂×r₂≤0.10λ₂:−0.033/(T ₂ λr ₂−0.037)+29.99≤θ≤−0.050/(T ₂ λr ₂−0.043)+32.45  (2). 4.The elastic wave device according to claim 1, wherein y of the Eulerangles (φ, θ, ψ) of the LiNbO₃ substrate falls within a range from about−2° to about 2°.
 5. The elastic wave device according to claim 1,wherein each of the first dielectric film and the second dielectric filmincludes silicon oxide as a primary component.
 6. The elastic wavedevice according to claim 2, wherein each of the first dielectric filmand the second dielectric film includes silicon oxide as a primarycomponent.
 7. The elastic wave device according to claim 1, wherein thefirst elastic wave resonator is a series arm resonator; the secondelastic wave resonator is a parallel arm resonator; and a ladder filterincludes at least the first elastic wave resonator and the secondelastic wave resonator.
 8. The elastic wave device according to claim 1,wherein the elastic wave device is a duplexer including a transmissionfilter that includes the first elastic wave resonator, and a receptionfilter that includes the second elastic wave resonator.
 9. The elasticwave device according to claim 1, wherein the first elastic waveresonator and the second elastic wave resonator each include a frequencyadjustment film.
 10. The elastic wave device according to claim 9,wherein the frequency adjustment film includes silicon nitride oraluminum oxide.
 11. The elastic wave device according to claim 1,wherein the thickness of the first dielectric film is thicker than thethickness of the second dielectric film.
 12. The elastic wave deviceaccording to claim 1, wherein each of the first IDT electrode and thesecond IDT electrode is a single-layer metal film or a laminated metalfilm in which two or more kinds of metal films are laminated.
 13. Theelastic wave device according to claim 1, wherein each of the first IDTelectrode and the second IDT electrode is a laminated metal filmincluding a close contact layer, the main electrode, a first closecontact layer, a conductive auxiliary film, and a second close contactlayer that are laminated in this order from a side of the LiNbO₃substrate.
 14. The elastic wave device according to claim 2, wherein ψof the Euler angles (φ, θ, ψ) of the LiNbO₃ substrate falls within arange from about −2° to about 2°.
 15. The elastic wave device accordingto claim 11, wherein each of the first dielectric film and the seconddielectric film includes silicon oxide as a primary component.
 16. Theelastic wave device according to claim 2, wherein the first elastic waveresonator is a series arm resonator; the second elastic wave resonatoris a parallel arm resonator; and a ladder filter includes at least thefirst elastic wave resonator and the second elastic wave resonator. 17.A high frequency front-end circuit comprising: the elastic wave deviceaccording to claim 1; and a power amplifier.
 18. A communicationapparatus comprising: the high frequency front-end circuit according toclaim 17; and an RF signal processing circuit.
 19. The high frequencyfront-end circuit according to claim 17, wherein the elastic wave deviceoperates as a duplexer.